Shelf unit



FIG. 1 is a front perspective view of a shelf unit showing our design.

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is a right side view thereof. 

The ornamental design for a shelf unit, substantially as shown. 